biopotential electrodes class8 9

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ECE 711 Biomedical Instrumentation

Origin of Biopotentials

Class 8

1Biomedical Instrumentation Dept of E & C Engg, NMAMIT


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Resting Potential & Action Potential

Bioelectric potentials are produced as a result ofelectrochemical activity of certain class of cells, knownas excitable cells , that are components of nervous,muscular or glandular tissue.

Electrically they exhibit a resting potential , and whenappropriately stimulated, an action potential .

The resting potential of the internal medium lies in therange of -40 to -90mV, relative to the external medium.

Biomedical Instrumentation Dept ofE & C Engg, NMAMIT

2


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Recording Action Potential

Biomedical Instrumentation Dept of E & C Engg, NMAMIT 3

John G WebsterCh 4


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Nernst Equation: Equilibrium Potential


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Goldman-Hodgkin-Katz (GHK)Formulation


which is close to typical measured values for the restingmembrane potential in frog skeletal muscle


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Biopotential Electrodes

Class 9



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1. Electrodes and sensors are used to detect biopotentials Half-cell potential Ag/AgCl Electrodes

2. Electrode Behavior and Circuit Models

3. Electrode Skin Interface

4. Motion Artifacts

5. Commonly used body surface electrodes Metal plate electrodes Suction electrodes Floating electrodes Flexible electrodes


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3. Electrode-Skin Interface



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3. Electrode-Skin InterfaceCircuit Model



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4. Motion Artifacts: Electrode/Gel-SkinContact

Electrode moves Charge distribution gets spoiled

Charge distribution gets disturbed Signal goes wild !

Signal goes wild Measurement goes bad

Measurement goes bad Risk to patient, since not diagnosed correctly!

Using non-polarizable electrodes (Ag/AgCl) reduce the low frequencynoise created by motion artifacts

ECG, EEG should use such electrodes (it can be filtered out of EMG)

However, the gel-skin contact also creates motion artifacts, and theAg/AgCl electrodes cant do damn anything about it!

What to do?Biomedical Instrumentation Dept of

E & C Engg, NMAMIT12


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5. Bioelectric Signals & Their Sources



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5. Commonly Used Biopotential Electrodes1. Metal plate electrodes

Large surface: Ancient, therefore still used, ECG Metal disk: EMG, EEG smaller diameters, w/stainless steel, platinum or gold

coated motion artifacts

Disposable foam-pad: Cheap !, m i n i m u m prep time Hospitals, ECG

2. Suction electrodes No straps or adhesives required, precordial (chest) ECG, can only be used

for short periods only

3. Floating electrodes Their metal disk is recessed, swimming in the electrolyte gel, so it is not in

contact with the skin reduces motion artifact4. Flexible electrodes

Since body contours are often irregular, regularly shaped rigid electrodesmay not always work, particularly with infants. Polymer or nylon with silverdeposits, or carbon filled silicone rubber in the form of a thin film (Mylar film)

5. Internal electrodes Biomedical Instrumentation Dept ofE & C Engg, NMAMIT 14


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1. Body-Surface Biopotential Electrodes


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a) Metal-plate electrode used for application

to limbs.b) Metal-disk electrode applied with surgicaltape.c) Disposable foam-pad electrodes, often usedwith ECG


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2. Suction Electrodes


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2. Suction Electrode: Fetal ECG



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FETAL ECG IN LABOR

Biomedical Instrumentation Dept of E & C Engg, NMAMIT18


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3. Floating Electrodes



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4. Flexible Electrodes



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5. Internal Electrodes



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References Chapter 1, 2, Chapter 4, 5, John G. Webster,

http://www.unc.edu/~finley/BME422/Webster/c04.pdf

http://users.rowan.edu/~polikar/CLASSES/ECE404/index_files/lectures.htm

Newman, MR, http://www.fis.uc.pt/data/20062007/apontamentos/apnt_134_5.pdf

ECG: http://www.ambulancetechnicianstudy.co.uk/ecgbasics.html#.U_nc9qP4Zdg


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http://www.unc.edu/~finley/BME422/Webster/c04.pdfhttp://users.rowan.edu/~polikar/CLASSES/ECE404/index_files/lectures.htmhttp://www.fis.uc.pt/data/20062007/apontamentos/apnt_134_5.pdfhttp://www.fis.uc.pt/data/20062007/apontamentos/apnt_134_5.pdfhttp://users.rowan.edu/~polikar/CLASSES/ECE404/index_files/lectures.htmhttp://www.unc.edu/~finley/BME422/Webster/c04.pdf


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Class 10


ECG Leads - Views of the Heart


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ECG


Chest LeadsV1 & V2V3 & V4V5 & V6

View

Right VentricleSeptum/Lateral Left Ventricle

Anterior/Lateral LeftVentricle

) l d f l l k


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a). Electrodes for ECG: Atrioventricular Block


(a) Complete heart block . Cells in the AV node are dead and activity cannot pass from atria to ventricles.Atria and ventricles beat independently, ventricles being driven by an ectopic (other- than-normal)pacemaker. (b) AV block wherein the node is diseased (examples include rheumatic heart disease andviral infections of the heart).


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ECG

b) El d f El i


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b). Electrodes for Electroretinogram


b) El d f El i


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b). Electrodes for Electroretinogram


A Typical Vertebrate ERG Waveform in Response to a 2s light flash

) El d f EEG


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c). Electrodes for EEG


Fig. The electroencephalographic changes that occur when a

human subject goes to sleep


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References Chapter 1, 2, Chapter 4, 5, John G. Webster,

http://www.unc.edu/~finley/BME422/Webster/c04.pdf

http://users.rowan.edu/~polikar/CLASSES/ECE404/index_files/lectures.htm

Newman, MR, http://www.fis.uc.pt/data/20062007/apontamentos/apnt_134_5.pdf ECG: http://www.ambulancetechnicianstudy.co.uk/ecgbasics.html#.U_nc9qP4Zdg

Biomedical Instrumentation Dept ofE & C E NMAMIT

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http://www.unc.edu/~finley/BME422/Webster/c04.pdfhttp://users.rowan.edu/~polikar/CLASSES/ECE404/index_files/lectures.htmhttp://www.fis.uc.pt/data/20062007/apontamentos/apnt_134_5.pdfhttp://www.fis.uc.pt/data/20062007/apontamentos/apnt_134_5.pdfhttp://users.rowan.edu/~polikar/CLASSES/ECE404/index_files/lectures.htmhttp://www.unc.edu/~finley/BME422/Webster/c04.pdf

biopotential electrodes class8 9

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